An in vitro transcription-translation system has been developed with intact DNA templates and DNA restriction fragments to study the control mechanism operating in the biotin operon. Conditions have been determined to demonstrate divergent transcription. BIBLIOGRAPHIC REFERENCES: Eisenberg, M.A., Mee, B., Prakash, O., and Eisenberg, M.R., Properties of alpha-Dehydrobiotin Resistant Mutants of Escherichia coli K-12, J. Bact., 122, 66, 1975. Eisenberg, M.A., The Mode of Action of alpha-Dehydrobiotin, a Biotin Analogue, J. Bact., 123, 248, 1975.